Environmental impact of roads

The environmental impact of roads (both positive and negative) include the local effects of highways (public roads) such as on noise, water pollution, habitat destruction/disturbance and local air quality; and the wider effects which may include climate change from vehicle emissions. The design, construction and management of roads, parking and other related facilities as well as the design and regulation of vehicles can change the impacts to varying degrees. Roads are known to cause significant damage to forests, prairies, streams and wetlands. Besides the direct habitat loss due to the road itself, and the roadkill of animal species, roads alter water-flow patterns, increase noise, water, and air pollution, create disturbance that alters the species composition of nearby vegetation thereby reducing habitat for local native animals, and act as barriers to animal movements.

Roads can have both negative and positive effects on air quality.

Air pollution from fossil (and some biofuel) powered vehicles can occur wherever vehicles are used and are of particular concern in congested city street conditions and other low speed circumstances. Emissions include particulate emissions from diesel engines, NO_x,volatile organic compounds,carbon monoxide and various other hazardous air pollutants including benzene. Concentrations of air pollutants and adverse respiratory health effects are greater near the road than at some distance away from the road.Road dust kicked up by vehicles may trigger allergic reactions.Carbon dioxide is non-toxic to humans but is a major greenhouse gas and motor vehicle emissions are an important contributor to the growth of CO₂ concentrations in the atmosphere and therefore to global warming.

...
Wikipedia